The present invention relates to traffic signals. In particular, the invention relates to controllers for light-emitting diode (LED) based traffic signals.
The main objective of a traffic signal arrangement (FIG. 1) is to coordinate vehicular flow sequencing the right of way in an orderly manner for vehicles that cross or intersect each other.
The electronics equipment to control the traffic signals that are installed throughout the world includes a set of equipment 101 to 106 housed in a standard rack mounted near the street crossing that delivers power to each signal or group of signals. This is known as a xe2x80x9ctraffic signal controller systemxe2x80x9d which includes as its main elements a controller 101, 103, 104 that coordinates the timing of the ON and OFF state for each signal or group of signals 118 and 119 and a monitoring system 102, 105, 106 for safety purposes. Signals 118 and 119 are generally parts of a traffic signal array that is mounted on a pole in the intersection. The AC/DC signal converters 105, 106 are used to convert the AC signals on lines 108 and 109 into DC signals 114, 115 appropriate for monitoring by the monitoring system 102.
Because any malfunction (hardware or software) of any equipment inside the traffic signal controller system may cause a traffic accident, current systems have an autonomous and independent monitoring system 102 that senses the state (ON or OFF) of each signal 118, 119 (that may represent a group of signals) to determine if this is an allowed safe state. If an unsafe state is detected the monitoring system may send a disable signal 116 to the central controller 101 to shut down the controller or to enter some sort of safety default, such as flashing the red signal. An example of an unsafe state would be green or yellow lights on two crossing streets of an intersection turned on at the same time.
Essentially, in these systems for each signal 118, 119 there exists wiring for power 107, 108, 109 and wiring for monitoring 110, 111 associated with each light signal controlled by the traffic signal controller system forming a star topology.
The above mentioned topology becomes complex and expensive because of the large number of power and monitoring cables employed and the circuitry 103, 104, 105, 106 associated with each set of wires for each signal or group of signals.
An attempt may be made to simplify this state of the art equipment by using a unique power line in a bus (or loop) configuration and by delivering control signals to set the ON and OFF state at individual signals. Although this would save power lines, such a system would still require an additional communications network and a CPU controlled device at each signal light position to manage/monitor the ON and OFF state. In and of itself such a bus based control scheme does not preclude simultaneous conflicting ON states. Therefore a significant simplification would not be achieved because this system, being intrinsically unsafe, would still require the use of individual wiring from each signal to the monitoring system.
The emerging LED technology applied to traffic signals offers an outstanding energy saving and maintenance cost reduction due to their low operational temperature, monochromatic light emission and extraordinary life expectancy or mean time between failure (MTBF). New kinds of LED devices especially designed for the traffic signals market have been emerging lately and many products have been developed in order to retrofit this technology to the existing traffic signal controllers. But, it is clear that the state of the art in traffic signal control systems has not yet adapted to this new traffic signal technology, hence new control systems, devices, and methods will be described here that take advantage of the technical benefits these new LED signal devices offer.
The present invention solves the above-noted problems (and other problems more fully discussed in the relevant sections below) by providing an apparatus for controlling traffic signals that includes a control unit and a plurality of traffic signal arrays. The control unit includes a power supply that supplies direct-current power. The control unit also includes a high-efficiency AC-to-DC converter. The present invention uses the power polarity features of polar devices to control traffic signals, resulting in lessened cable requirements and intrinsic failsafe operation.